This sounded like what I needed, but Coloration failed to process the .tmTheme file, and looking at the github tracker I found this comment: "coloration sets highlighting colors using #rrggbb format which is not supported by regular vim in terminal, only graphical vim versions..."
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SymmetricApr 16 '12 at 2:56

See this pastebin: not only it processes Aptana Studio.tmTheme successfully but it also converts colors to work both in 256colors-capable terminal emulators (ctermbg=248) and GVim/MacVim (guibg=#a7a7a7). As I see it, this tool and the process I've detailed above are the only practical solution to your "problem" and, judging by the :color aptana I've just typed in Vim, a very effective one.
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romainlApr 16 '12 at 3:10

Here is a screenshot. It's CLI Vim, running in Gnome terminal on Ubuntu 10.10. On the left is the original theme exported from Aptana, on the right is the Vim colorscheme as processed by Coloration (with the name changed by hand) and the active colorscheme is aptana.
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romainlApr 16 '12 at 3:24

Awesome, thanks for that. I'm not sure why Coloration is failing for me; it still gives me the error "This file doesn't look like xml plist file containing Textmate theme.". I appreciate you doing the legwork on this one :)
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SymmetricApr 16 '12 at 3:42

What version of Aptana do you use? Mine (downloaded yesterday from aptana.com/products/studio3) is Aptana Studio 3, build: 3.0.9.201202141038.
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romainlApr 16 '12 at 3:56